1. Field of the Invention
The invention concerns a liquid container and a method for the cooling of a liquid in a container by means of a sorption device.
2. Description of the Prior Art
Sorption apparatuses are apparatuses in which a liquid or solid sorbent absorbs a second, higher-boiling agent, the working agent, in the form of a vapor, with the release of heat. The working agent thereby evaporates in an evaporator with the absorption of heat. After the sorbent is saturated, it can be desorbed, once more, by supplying heat. The working agent thereby evaporates from the sorbent. The working agent vapor can be reliquified and subsequently evaporated, once again, in the evaporator.
Sorption apparatuses for cooling with solid sorbents are known from EP 0 368 111 and DE-OS 34 25 419. Sorbent containers, filled with sorbents, thus draw off the working agent vapor that is formed in an evaporator and absorb it in the sorbent charging with the release of heat. The sorption heat must thus be conducted away from the sorbent charging. The cooling apparatuses can be used for cooling and keeping warm foods in thermally insulated boxes.
The sorption cooling system known from EP 0 368 111 consists of a portable cooling unit and a stationary charging station, which can be separated from it. The cooling unit consists of an adsorption container, filled with a solid sorbent, and an evaporator, which contains a liquid working agent and a heat exchanger embedded therein. The evaporator and the adsorption container are connected to one another via a vapor conduit, which can be sealed off. Liquid media, which are cooled by the temperature-regulated opening and closing of the sealing-off device to the desired temperature level, flow through a heat exchanger embedded in the evaporator. After the adsorption agent is saturated with the working agent, it can be heated in a charging station. The working agent vapor thus flowing off is reliquified in the evaporator. The condensation heat is thereby conducted off through cooling water, which must flow through the embedded heat exchanger. The sorption cooling system is expensive to produce because of the embedded heat exchanger and the temperature regulation and too complicated to be used practically by the untrained layperson.
The goal of the invention is to provide a more easily handled and cheaper apparatus in comparison to the state of the art.
The goal is attained by the characterizing features of the independent claims. The dependent claims indicate other inventive method steps and apparatuses.
A sorption apparatus in accordance with the invention accordingly contains a sorbent within a sorbent container, a vapor conduit, which can be sealed off, and a liquid working agent within an evaporator. The evaporator is in good thermal contact with a liquid, which is held in a container. The components are firmly connected to one another and remain this way even during all of the processing steps.
During the regeneration phase, the sorbent is heated and the working agent vapor desorbed. It flows through the sealable vapor conduit to the evaporator and condenses out there. The condensation heat is absorbed by the liquid in the container with an increase in temperature. At the end of the regeneration, the supply of heat to the sorbent is interrupted. The desorption of additional working agent vapor ends in this way. The desorbed working agent is found in liquid form in the evaporator. The vapor conduit is sealed off. The sorbent cools to ambient temperature by the release of heat via the walls of the sorbent container.
To introduce the cooling phase, the sealed-off vapor conduit is opened. The working agent vapor can then flow from the evaporator into the sorbent container and be exothermally absorbed by the sorbent. The evaporating working agent quantity in the evaporator and the liquid surrounding it are cooled. In order to produce the maximum amount of cooling in a short time, the sorbent must be actively cooled. A particularly intensive cooling effect is attained if the absorption container is surrounded by a sufficiently large water mass which absorbs the sorption heat, or a smaller quantity of water can evaporate with the absorption of heat by the sorbent container wall. Advantageously, the container walls should be cooled to temperatures of less than 50xc2x0 C. Then sufficiently low temperatures are possible in the evaporator.
Only the liquid volume that is found around and below the evaporator is cooled, in accordance with the invention. The upper liquid volume remains close to the starting temperature because of the lower density and the lower heat conduction of liquids. By suitably positioning and shaping the evaporator, the liquid volume to be cooled can be preselected. In actual practice, a more rapid cooling of the lower liquid quantity, which is then removed first, is attained in this way. The upper liquid quantity is first cooled, when it drops into the area of the evaporator, by tapping the cooled quantity.
In general, the container is cleaned before it is refilled. For this purpose, cleaning and rinsing liquid is conducted into the container and, as a rule, again drained when the container is tilted. The evaporator is shaped in such a way that the container can be emptied in all cleaning processes without problem and without leaving behind any rinsing agent residue. The evaporator walls, which are in contact with the liquid, are smooth and without retention indentations. Lens-shaped and cylindrical configurations have proved useful.
The interior space of the evaporator should be shaped in such a way that the aqueous filling, which is removed by evaporation, wets the entire surface of the wall for as long as possible, so as to utilize the entire heat exchanger surface. In accordance with the invention, retention devices, such as hygroscopic surface coatings or bowl-shaped components are used for this purpose.
The use of zeolite/water as the adsorption substance is particularly advantageous. Zeolite is a crystalline mineral, which consists of a regular framework structure of silicon and aluminum oxides. This framework structure contains small cavities, in which water molecules can be adsorbed with the release of heat. Within the framework structure, the water molecules are exposed to strong field forces which liquefy the molecules in the lattice and bind them in a phase similar to a liquid. The strength of the binding forces acting on the water molecules is dependent on the water quantity already contained in the framework structure and the temperature of the zeolite. For practical use, up to 25 g water can be adsorbed per 100 g zeolite. The cooling volume which can be produced is thereby sufficient to cool 1 L water 14K. Zeolites are solid substances without a disturbing heat expansion in the sorption or desorption reaction. The framework structure is freely accessible for the water vapor molecules from all sides. The apparatuses can therefore be used in any position.
The use of water as the working agent permits the reduction of the required regulation expenditure to a minimum. Upon evaporating water under a vacuum, the water surface cools to 0xc2x0 C. and freezes to ice with continued evaporation. This ice layer grows rapidly until the pressure decline, which occurs due to the ice layer, stops the growth. The ice layer can be used advantageously to regulate the liquid temperature. With a low heat supply, the ice layer grows until a very large supply of heat melts it. By the natural formation of ice, the heat transfer from the liquid to the evaporator is reduced, so that the liquid does not cool below 0xc2x0 C. and usually, remains at 4-5xc2x0 C.
Substances that lower the freezing point can also be admixed to the aqueous evaporator content if the tapping temperature of the liquid is to be lowered below 4xc2x0 C. or an icing over of the evaporator filling is to be prevented.
Other sorbent pairings, however, can also be used, in which the sorbent is solid and also remains solid during the sorption reaction. Solid sorbents have low thermal conductivity and poor heat transfer. Since the heat transfer of gaseous media (air, waste gases) to the sorbent container lies within the same order of magnitude, heat exchangers without ribs, such as plates, tubes, or even corrugated tubing, are recommended, in principle. Some solid sorbents, such as zeolites, are also stable enough to compensate for outside excess pressures on thin-walled heat exchanger surfaces. Additional reinforcements or thick-walled heat exchanger surfaces are therefore unnecessary. Since with the use of water as the working agent the sorption apparatus is under vacuum and no gases should penetrate into the system during the entire period of functioning, the known vacuum-tight components are to be preferred for the sealing-off device. For manual actuation, ducts which are sealed off by means of metal bellows have proven particularly useful.
The absorption container which is being heated during the exothermal absorption reaction should be thermally decoupled from the container, so as to avoid a reheating of the liquid. Advantageously, the sorbent container can be placed below the container or above the container. In the first case, it can be cooled by immersion into a basin filled with water, and for the regeneration, it can be placed on an electrically heated heating plate. In the second case, warm air rising from the absorption container cannot sweep the container and reheat the already cooled liquid.
For an economical mode of operation, sorbent temperatures of 200-300xc2x0 C. are recommended during the regeneration and of 40-80xc2x0 C. during the absorption. Since zeolite granules especially have low thermal conductivity, the absorption container must be laid out in such a way that the heat conduction path for the reacted heat quantities does not exceed about 3 cm. All apparatuses which attain the required temperature level and do not unnecessarily heat the liquid in the container are suitable as heat sources for the regeneration. Electrically heated plates or cartridges, which are adapted to the configuration of the sorbent containers are advantageous. The heating can, for example, also be arranged for several liquid coolers in one pallet, so as to utilize production-influenced storage times for the regeneration after the filling of the containers. Heating apparatuses which heat the sorbent charging via radiant or inductive heat (eddy currents) are also advantageous. Of course, it is also possible to permanently connect the heating device with the absorption container and also to leave the device on it when transporting a portable liquid cooler.
It may also be advantageous to optimize the configuration of the sorbent container for the release of heat during the absorption phase. In the case of the release of heat to the surrounding air, large, flow-conducive heat exchanger surfaces are preferred, whereas in the case of evaporative or water cooling, holding basins or water-storing surface coverings (for example, paper banderoles with advertisements).
No special demands are made on the size and configuration of the containers. Thus, all containers common at present (for example, vats, containers, cans, open containers, foil sacks, multilayer packagings, plastic containers, canisters, hobbocks, bottles, jugs, and so forth) which are suitable for flowable filling materials can be used, as long as the sorption apparatus can be coupled for proper operation.
Three liquid coolers in accordance with the invention are depicted in the drawing.